This invention relates in general to gas compressors and in particular relates to an unloading valve device for use with gas compressors of the type used for driving medical respirators.
A critical problem in gas compressors is the requirement of unloading trapped or deadhead pressure from the working chamber or cylinder head when the compressor is shut down so that it can be more easily restarted at a later time. In many cases the deadhead pressure which is developed upon shutdown is of such magnitude that it becomes extremely difficult or even impossible to restart the compressor unless the deadhead pressure is relieved. This condition particularly occurs when a compressor is stopped at a point in its cycle where the piston or diaphram is approaching its top dead center position. Where the compressor is electrically driven, a serious thermal overload in the motor can occur if the deadhead pressure is not relieved.
Heretofore various devices have been employed in an attempt to relieve the deadhead pressure from compressors. Among these devices are unloading valves such as whisker valves or centrifugal switches which are arranged to bleed pressure from the compressor's working chamber upon shutdown. However, such prior devices are relatively complex and expensive in design and construction, and have not been completely satisfactory in operation. A need has therefore been recognized for an improved means for unloading deadhead pressure from compressors.